Multi optically-coupled channels module and related methods of computation

ABSTRACT

An integrated optical module is provided. The optical module includes multi optically-coupled channels, and enables the use thereof in an Artificial Neural Network (ANN). According to some embodiments the integrated optical module includes a multi-core optical fiber, wherein the cores are optically coupled.

FIELD OF THE INVENTION

The invention, in some embodiments, relates to optical computationaldevices and more particularly, but not exclusively, to optical hardwareimplementations of artificial neural networks.

BACKGROUND OF THE INVENTION

Recent years have seen an increase in efforts to develop and implementunconventional computation, that is, non-semiconductor-basedcomputation. These efforts are motivated in part by a breakdown ofMoore's law resulting in a slowdown in the rate of increase ofcomputational power of conventional computers, i.e. semiconductor basedcomputers. Some of these efforts are directed at optical computation.That is to say, computation based on manipulation of light, typicallylasers, rather than electronic currents as in semiconductor-basedcomputation.

SUMMARY OF THE INVENTION

Aspects of the invention, in some embodiments thereof, relate to opticalcomputational devices. More specifically, but not exclusively, aspectsof the invention in some embodiments thereof relate to optical hardwareimplementations of artificial neural networks (ANNs).

Optical computation offers a number of advantages as compared toconventional computation. Optical computational systems may beconsiderably faster than conventional computational systems, becauseelectric currents travel slower than the speed of light. Opticalcomputational systems may also have considerably higher thermalefficiency compared to conventional electronic systems. Yet,state-of-the-art optical computational systems are typically larger thantheir semiconductor-based counterparts.

Hybrid optical-electronic computation attempts to combine the advantagesof optical and conventional computation by implementing somecomputational components optically and some electronically, withinformation being typically transferred optically. However, instate-of-the-art hybrid optical-electronic computational systems about30% of the total energy consumed is spent on the inter-conversion ofoptical signals to electric currents, rendering such hybrid systemswasteful as compared to all-optical computational systems.

In view of the foregoing disadvantages inherent in the above-mentionedstate-of-the-art computational systems and specifically opticalcomputational systems, embodiments of the invention presented hereininclude an integrated multi-channel optical module for controllablymapping sets of input light signals onto sets of output light signals. Amodule or a unit or a system is said to be “integrated” if the module isfabricated as a whole, as opposed to being assembled of individuallyfabricated components. A mapping of a set of input signals onto a set ofoutput signals means that the module produces a set of output signals inresponse to an input of a set of input signals, and the power of eachoutput signal is a non-trivial function of the powers of the inputsignals. By “non-trivial” it is meant that the output signal is actuallydependent on at least two input signals, namely that a variation of thepower of each of the at least two input signals independently varies thepower of the output signal.

The optical module comprises at least two optical channels configured toallow directional propagation of light therein, wherein at least one ofthe optical channels is an amplification channel configured to allowamplification of light propagating therein by a controllableamplification factor. The optical module further comprises at least twoinput ports, individually associated with the at least two opticalchannels, configured to allow transmission of input light signals intothe optical channels. The optical module further comprises at least oneoutput port optically associated with one of the at least two opticalchannels, configured to allow emission of an output light signal fromthe one optical channel. The optical module further comprises at leastone control port functionally associated with the amplification channeland configured to allow inputting a control signal to the amplificationchannel to determine the amplification factor. The optical channels areoptically coupled so that a power of an output light signal emitted fromthe output port is a function of powers of the at least two input lightsignals transmitted through the at least two input ports.

According to some embodiments, the optical module of the invention maycomprise hundreds of thousands of optically coupled optical channels.Such a high number of optical channels may allow for implementation ofcomplex and cumbersome computations and tasks, using for example NeuralNetworks strategies as detailed and explained herein below. According tosome embodiments, the optical module comprises a multi-core fiber havinga length as low as about one centimeter, whereas time of travel of lightalong the fiber is on the order of 100 pico-seconds (10{circumflex over( )}−10 sec). Accordingly, a complete task suitable for a neuralnetwork, such as image recognition, may be completed on such a shorttime scale comparable to the time of travel of light along the fiber, asis further explained below. Furthermore, by employing optical modulessuch as multi-core fibers which contain tens of thousands or hundreds ofthousands of cores or photonic crystals comprising hundreds of thousandsof optically couples channels, extremely complex and cumbersomecomputations may be effected substantially over time scale comparable tothe time of travel of light through the channels. Hence, even using e.g.multi-core fibers of typical lengths on the scale of meters—e.g. 1 meterlength or even 10 meters length—may provide a huge computation speed upcompared to the speed offered by current technology.

The integrated optical module of the invention thus offers considerableadvantages compared to existing optical computation system utilizingfree-space optics: an integrated optical module may be easily packagedin a small and handy package, or as a single component on a printedcircuit board or on a chip. As a result, such an integrated module pavesa way for compact systems capable of performing highly complexcomputations. The integrated module further offers enhance modularity asseveral modules may be packaged together to build up a more complexsystem. Small dimensions of the integrated module further minimizeslight losses which hare typically associated with free-space optics,leading in turn to enabling using relatively low-power sources and hencelittle heat dissipation and energy loss. Lastly, the integrated opticalmodule of the invention may be manufactured using currently availablematerials and employing currently available manufacturing techniques, asexplained and detailed below, thereby rendering the module of theinvention compatible with currently available technologies andperipheral devices such as light sources and light detectors, makingindustrial employment of the module of the invention highly attractive.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention are described herein with reference tothe accompanying figures. The description, together with the figures,makes apparent to a person having ordinary skill in the art how someembodiments may be practiced. The figures are for the purpose ofillustrative description and no attempt is made to show structuraldetails of an embodiment in more detail than is necessary for afundamental understanding of the invention. For the sake of clarity,some objects depicted in the figures are not to scale.

In the Figures:

FIG. 1 depicts an embodiment of an integrated optical module, comprisestransmission channels and amplification channels, according to an aspectof the invention.

FIG. 2A schematically depicts a two-core optical fiber embodiment of theinvention;

FIG. 2B schematically depicts a cross-sectional view of the two-coreoptical fiber of FIG. 2A;

FIG. 3A schematically depicts a multi-core optical fiber embodiment ofthe invention;

FIG. 3B schematically depicts the multi-core optical fiber of FIG. 3A ina preferred mode of operation;

FIG. 4 schematically provides a detailed view of the spatial arrangementon the x-y plane of the cores of the multi-core fiber of FIG. 3A;

FIGS. 5A-5G schematically depict transfer of light signals by evanescentwave coupling along sequences of cores from input to output, in 7cross-sections of the multi-core fiber of FIG. 3A along the z axis;

FIG. 6 schematically depicts a system on a chip comprising a multi-coreoptical fiber of the invention;

FIG. 7 schematically depicts a system configured for inputting a largenumber of input light signals to a multi-core optical fiber of theinvention;

FIG. 8A schematically depicts an embodiment of a learning systemcomprising a multi-channel optical module of the invention, in anembodiment of a learning mode of operation;

FIG. 8B schematically depicts the learning system of FIG. 8A in anembodiment of an implementation mode of operation;

FIGS. 9A and 9B schematically show light intensity of λ₁=1,550 nm lightin cores of the multi-core optical fiber of FIG. 3A in a particular modeof operation along cross-sections at z, y, x=14.5 μm and at z, y, x=18μm, respectively;

FIGS. 9C and 9D schematically show light intensity of λ₂=980 nm light incores of the multi-core optical fiber of FIG. 3A in a particular mode ofoperation along cross-sections at z, y, x=14.5 μm and at z, y, x=18 μm,respectively;

FIG. 9E presents a power scale, wherein the level of power isrepresented by a gray-level scale;

FIG. 9F depicts the power of light signals of wavelength λ₁=1,550 nm ineach of the cores at four cross-sections of the multi-core optical fiberof FIG. 3A in the mode of operation of FIGS. 9A and 9B;

FIG. 9G depicts the power of light signals of wavelength λ2=980 nm ineach of the cores at four cross-sections of the multi-core optical fiberof FIG. 3A in the mode of operation of FIGS. 9C and 9D;

FIG. 10A schematically depicts the spatial arrangement of the cores inthe multi-core optical fiber of FIG. 3A in a mode of operationdemonstrating classification;

FIG. 10B shows results of a simulation of the mode of operation of FIG.10A demonstrating classification of three 8-bit strings;

FIGS. 10C and 10D show results of two control simulations, respectively,demonstrating the specificity of the amplification signals thatdemonstrated classification in FIG. 10B.

FIG. 10E shows a comparison of output light signals powers in the sixoutputs of the multi-core optical fiber of FIG. 3A, for the three setsof amplification signals used in FIGS. 10B-10D, respectively;

FIG. 10F shows results of a simulation wherein all possible eight bitstrings comprising four zeros and four ones were encoded and transmittedinto the multi-core optical fiber of FIG. 3A with the set ofamplification signals used in FIG. 10A;

FIG. 11A presents results of a simulation demonstrating classificationusing the multi-core optical fiber of FIG. 3A with amplification coreswith amplification of 41 dB/m;

FIG. 11B reproduces the results of the simulation of FIG. 10B (at z=9mm), for comparison;

FIG. 12 schematically depicts a transverse cross-section of a photoniccrystal fiber embodiment of the invention;

FIG. 13 schematically depicts a photonic crystal slab embodiment of theinvention, and

FIG. 14 schematically depicts a 3D photonic crystal embodiment of theinvention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The principles, uses and implementations of the teachings herein may bebetter understood with reference to the accompanying description andfigures. Upon perusal of the description and figures present herein, oneskilled in the art is able to implement the teachings herein withoutundue effort or experimentation.

In the following, two or more magnitudes are said to be “comparable” ifthe largest of the magnitudes is not greater than twice the smallest ofthe magnitudes; two or more magnitudes are said to be of a “same orderof magnitude” if the smallest of the magnitudes is no smaller than onetenth the largest of the magnitudes.

As used herein “Set of elements” is defined as a group or collection ofone or more elements. A “sequence of elements” is defined as an orderedset of elements.

A mapping of a set of input signals onto a set of output signals meansthat the power of each output signal is a non-trivial function of thepowers of the input signals. By “non-trivial” it is meant that theoutput signal is actually dependent on at least two input signals,namely that a variation of the power of each of the at least two inputsignals independently varies the power of the output signal. In thefollowing, when an output signal is said to be dependent on inputsignals or to be a function of input signals, it is presumed for thesake of brevity, that such dependence is non-trivial.

A module or a unit or a system is said to be “integrated” if the moduleis fabricated as a whole, as opposed to being assembled of individuallyfabricated components.

As used herein, “channel” is defined as a spatially confined mediumallowing directional propagation of light therein, wherein the bordersof the medium determine the propagation direction of the light.

An Integrated Optical Module Embodiment

FIG. 1 depicts an embodiment of an optical module 100, according to anaspect of the invention. Optical module 100 comprises transmissionchannels 110 and amplification channels 120. For each channel, the localdirection of light propagation is denoted by a local z axis, and theperpendicular plane is denoted a local x-y plane. In the exemplaryembodiment depicted in FIG. 1, a generalized z axis 102 is common to allthe channels throughout the optical module. In optical module 100 lightgenerally propagates in the channels 110 and 120 along the z axis fromleft to right, however in some embodiments of the invention light maypropagate in one or more of the channels, and even in all of thechannels, in both directions parallel to the z axis. Optical module 100is an integrated module, and may be realized according to someembodiments by a multi-core optical fiber or for example by a photoniccrystal fiber, as is further detailed and explained herein below.Accordingly, optical module 100 may be assembled on a single piece ofsubstrate such as on a chip, as is further illustrated and detailedbelow.

Transmission channel 110 is configured to enable propagation of lightpassing therethrough along the channel, substantially withoutmodification of the light intensity (power). Parasitic losses, causingunavoidable decrease of light intensity along the channel, arepreferably minimized. Amplification channel 120 is configured to enablepropagation of light passing therethrough along the channel, and enablescontrolled amplification of the light intensity. “Amplification” hereinis used in a broad sense, covering both strict amplification involvingamplification factors greater than 1, and attenuation, involvingamplification factors between 0 and 1. Each amplification channel 120 isassociated with a control port 122 configured for receiving a controlsignal for determining a desired amplification factor in theamplification channel thereby controlling the amplification in thechannel.

At least two of the channels from the transmission channels 110 and theamplification channels 120 are optically associated, preferablyindividually, with input ports 130. Input port 130 is configured toenable transmission of a light signal into an associated channel (atransmission channel or an amplification channel), thereby inputtingsuch light signal to optical module 100. For example, an exposed end ofan optical fiber may function as an input port to the fiber. Lightsignals suitable for transmission into optical module 100 are furtherdescribed below.

At least one of the channels from both the transmission channels 110 andthe amplification channels 120 is optically associated with one or moreoutput ports 140. Output port 140 is configured to enable transmissionof a light signal from an associated channel, thereby outputting suchlight signal from optical module 100. For example, an exposed end of anoptical fiber may function as an output port to the fiber. Light signalstransmitted from optical module 100 through output port 140 may beoptically processed and/or detected by an optical detector as is furtherdetailed below.

At least one of the transmission channels 110 and at least one of theamplification channels 120 are optically coupled with one another.Optical coupling between channels is denoted in FIG. 1 by a dashed line150 between optically coupled channels. In FIG. 1, light generallypropagates from left to right, hence it should be understood that lightis transferred between two channels coupled by optical coupling 150,from the channel on the left-hand-side of the related dashed line to thechannel on the right-hand-side of the dashed line.

The Integrated Optical Module in Operation

Optical coupling between channels in optical module 100 forms sequences160 of optically coupled channels. Each sequence 160 comprises adistinct series of optically coupled channels, ordered according to thedirection of light propagation in the channels and the direction oflight transfer (through the optical coupling) from one channel to thenext. Hence, a first channel in each sequence 160 is associated with oneof the input ports 130, whereas a last channel in each sequence isassociated with one of the output ports 140. In FIG. 1, 3 sequences, 160a, 160 b and 160 c, are explicitly denoted for example. Sequence 160 acomprises, in the order by which light propagates therein, channels 160a 1, 160 a 2 and 160 a 3. Likewise, sequence 160 b comprises channels160 b 1, 160 b 2 and 160 b 3, and sequence 160 c comprises channels 160c 1, 160 c 2 and 160 c 3.

It should be noted that an individual channel may be common to more thanone sequence. For example, the first channel 160 a 1 in sequence 160 ais the first channel 160 b 1 in sequence 160 b. Likewise, the lastchannel 160 b 3 in sequence 160 b is also the last channel 160 c 3 insequence 160 c. It should therefore be understood that, according tosome embodiments, an input light signal (transmitted into optical module100 through one of the input ports 130) may affect the output lightsignals through one or more output ports 140. For example, the inputlight signal transmitted into channel 160 a 1 may affect the outputlight signals through channels 160 a 3 and 160 b 3. Likewise, an outputlight signal (transmitted from optical module 100 through one of theoutput ports 140) may be affected by the input light signals through oneor more input ports 130. For example, the output light signaltransmitted from channel 160 b 3 may be affected by the input lightsignal through channel 160 b 1 and by the input light signal throughchannel 160 c 1.

In operation, a set of input light signals from one or more respectiveexternal light sources (not shown) is transmitted, via input ports 130,into associated transmission channels 110 and amplification channels120, so that each of said channels receives a respective input lightsignal. Light signals may thus propagate through the sequences ofchannels along optical module 100. Intensities (powers) of light signalsthat are propagating simultaneously through the sequences 160 of opticalmodule 100 may be partially combined when one channel (that belongs totwo or more sequences) receives light from respective two or moreoptically coupled channels. Likewise, the power of a light signalpropagating in one channel may be split as the light signal istransferred to two or more channels (belonging to two or more sequences)that are optically coupled to the said channel.

Optical module 100 may thus enable establishing a mapping of input lightsignals to output light signals. Such mapping is partly defined by thepre-determined arrangement of sequences 160 in the optical module,namely by the combination and splitting of powers of light signals alongthe optical module, through optical coupling between channels, suchoptical coupling being pre-determined by the structure of the opticalmodule (e.g. the geometry of the arrangement of the channels, theoptical properties of the transmission channels and the amplificationchannels). The mapping may further be defined—and varied—by controllingthe amplification of each amplification channel in the optical module.In other words, each output signal O_(i) may be represented as afunction O_(i)=f(I₁, . . . I_(j), . . . I_(N) _(i) ) of the inputsignals I_(j). Here 1≤i≤N_(O), N_(O) being the number of outputs inoptical module 100 and 1≤j≤N_(I), N_(I) being the number of inputs inoptical module 100. More specifically, according to some embodimentseach output O_(i) may be represented as a weighted sum of the inputs:O _(i)=Σ_(j)(A _(j) ^(i) +B _(j) ^(i))I _(j),Where the A_(j) ^(i) are fixed, being pre-determined by the opticalcoupling between channels in the optical module, and the B_(j) ^(i) canbe modified by modifying the controllably selected amplification factorsin the amplification channels 120. It is emphasized that optical module100 is configured and operable to establish a non-trivial functionbetween the inputs and the outputs, namely that at least one output isnon-trivially (actually) dependent on at least two inputs.

A Two-Core Optical Fiber Embodiment

Multi-core optical fibers have been proposed as an improvedcommunication means to increase data transfer rate over a single fiber.In such a multi-core optical fiber, each core is used as an independentchannel for data transfer, which is, ideally, optically isolated fromother cores in the same fiber. Signal from one core leaking to a secondneighboring core generates noise in the second core, and therefore, asabsolute optical isolation may not always be achieved, very low signalleakage (low crosstalk) between cores is ever desired. Indeed, varioustechniques have been proposed to minimize crosstalk between cores inmulti-core optical fibers. These include fibers with high Δ (Δ being thedifference between the refractive indexes of the core material and thecladding), high core pitch (the pitch being the distance betweenneighboring cores) and employing hole- or trench-assisted core profiles.Thus, in existing multi-core optical fibers, crosstalk between cores istypically extremely low and commonly specified to be below apre-determined threshold (typical values being below −30 dB for 100 kmlong fibers), so as to ensure that the signal in one core contributes nomore than a specified contribution to the Optical Signal-to-Noise Ratio(OSNR) in a neighboring core. It follows that in existing multi-corefibers, the coupling length (between two adjacent cores) is much greaterthan the total length of the fiber, thus ensuring that, at maximum, onlya minute fraction of the signal power in one core transfers to aneighboring core.

In contrast to existing multi-core fibers (typically used for opticalcommunication), a multi-core optical fiber embodying the invention isrequired to demonstrate a well-determined, significant, non-vanishingoptical coupling between at least some of the cores. By the opticalcoupling being “well-determined” it is meant that the optical couplingis specified within a pre-determined range (namely between a low-end anda high-end of the range) as opposed to being specified to be just lowerthan a threshold. By the optical coupling being “significant” it ismeant that the low-end of the range is higher than the inverse of theSNR of a system in which the multi-core fiber is used. In other words,the optical coupling is such that a light signal that is transferredfrom a first core to a second core by such optical coupling, has, in thesecond core, an intensity (power) that is at least above, and preferablysignificantly above, the noise level of the system. Thus, in amulti-core optical fiber of the invention optical coupling between cores(that are determined to be mutually “optically coupled”) is high enough,to allow for a light signal transferred by optical coupling to behigher—preferably significantly higher—than the noise; whereas inexisting multi-core optical fibers, a light signal transferred byoptical coupling must be lower—preferably significantly lower—than thenoise. In some preferred embodiments of the invention, optical couplingbetween “optically coupled” cores is high enough to render the couplinglength comparable to the total length of the fiber. This means that thecoupling length is at maximum smaller than twice the length of thefiber. In some embodiments the coupling length may be equal or smallerthan the total length of the fiber. In some embodiments, especiallyembodiments comprising a multitude of optically coupled cores, thecoupling length may even be a small fraction of the total length of thefiber.

Optical coupling between cores in a multi-core optical fiber istypically realized through evanescent wave coupling. Evanescent wavecoupling is used here to denote a phenomenon wherein light transfersfrom a first medium to a second medium as an exponentially decaying wavethrough a third medium, separating the first medium from the secondmedium and having a lower refractive index than that of the first mediumand the second medium. Evanescent wave leakage between two lightpropagating mediums, e.g. two cores in an optical fiber, denotestransfer of light from one medium to the other due to evanescent wavecoupling.

Evanescent wave coupling between cores is strongly dependent on thecores geometrical parameters such as diameter and distance between thecores as well as on the mode of light propagation in the core. Forsubstantial evanescent wave coupling between cores, which is necessaryfor implementing the invention, optically coupled cores in a multi corefiber of the invention may be arranged at distances that are typicallysmaller than in conventional multi-core fibers wherein optical couplingbetween cores is undesired. For example, in fibers fabricated frommaterials commonly used in the art, substantial evanescent wave couplingbetween cores having a diameter of about 8 um for example, may beachieved when the distance between cores centers is smaller than about20 um, preferably when the distance between cores centers is smallerthan about 15 um, and more preferably when the distance is smaller thanabout 10 um. In contrast, in fibers where optical coupling is undesiredand therefore exists as a parasitic phenomenon, distance between coresis larger than e.g. 20 um and preferably larger than 30 um.

Another embodiment of the invention described herein is schematicallydepicted in FIG. 2A and FIG. 2B. FIG. 2A depicts a cylindrical two-coreoptical fiber 200. Two-core optical fiber 200 comprises a fiber body 204extending between a first fiber end 208 and a second fiber end 210.Fiber body 204 houses a first cylindrical core 220 and a secondcylindrical core 222. Each of cylindrical cores 220 and 222 extendslongitudinally from first fiber end 208 to second fiber end 210. A fibercladding 240 submerges cylindrical cores 220 and 222. Cylindrical cores220 and 222 may be made of e.g. glass, silicon, silica or plastic asknown in the art of optical fiber fabrication. Cladding 240 is made of amaterial having a refractive index lower than the refractive index offirst cylindrical core 220 and of second cylindrical core 222. Secondcylindrical core 222 is configured to amplify light signals travelingtherethrough. According to some embodiments, second cylindrical core 222may be doped to enable amplification. For example, cylindrical cores 220and 222 may be made of silica, and second cylindrical core 222 may bedoped with Erbium ions. First fiber end 208 and second fiber end 210 areconfigured to receive light transmitted thereto (through an input port)and to emit light therefrom (through an output port).

FIG. 2B schematically depicts a cross-sectional view of two-core opticalfiber 200 on a plane whereon first cylindrical core 220 and secondcylindrical core 222 extend. First cylindrical core 220 comprises afirst input port 250 on first fiber end 208 and a first output port 256on second fiber end 210. Likewise, second cylindrical port 222 comprisesa second input port 252 on first fiber end 208 and a second output port258 on second fiber end 210. Second cylindrical core 222 also comprisesa control port 262 on first fiber end 208.

Optical fiber 200 is configured to provide optical coupling betweencylindrical cores 220 and 222 by evanescent wave coupling. In otherwords, light propagating through either of cylindrical cores 220 and 222may transfer to the other core via evanescent wave coupling. For twocylindrical and parallel cores (extending from z=0 to z=L, where L isthe length of fiber body 204), a coupling efficiency over a core lengths≤L is defined as η(z=s)=P₂(z=s)/P₁(z=0), where P₁(z=0) is a power oflight transmitted into the first core at z=0, and P₂(z=s) is the powerof light in the second core at z=s under a condition that no light istransmitted into the second core, i.e. P₂(z=0)=0. If the light in thesecond core is not amplified, then all the light propagating through thesecond core is transferred light. Under some conditions, the couplingefficiency may increase and then decrease as a function of z, because,at high z values, some light transfers back from the second core to thefirst core. A coupling length/is defined as the smallest z coordinatewhere the coupling efficiency reaches a maximum.

Second cylindrical core 222 is configured to enable controlledamplification of light having a first wavelength λ1 propagatingtherethrough, by transmitting into the core light having a secondwavelength λ2 (e.g. a pump light signal). The λ₂ light may betransmitted into the core through control port 262 which may be selectedto be the one of the exposed ends of cylindrical core 222 at eitherfirst fiber end 208 or second fiber end 210.

According to some embodiments, second cylindrical core 222 may be dopedto allow such controlled amplification. In a doped core, the dopant ionsare excited following absorption of λ₂ photons, and relaxation of theexcited ions is facilitated by λ₁ photons through a process known asstimulated emission. In the relaxation process the excited ions emitadditional λ1 photons with the same phase as the facilitating λ₁photons, thereby increasing the power of the already present λ₁ light inthe core. By controlling the power of the λ2 light transmitted intocylindrical core 222, the level of amplification of the λ1 light may becontrolled. It is noted that the optical coupling between the cores isfixed and constant, being determined by the structure of the two-corefiber, and other fixed parameters, as explained above. It is furthernoted that the amplification of the λ1 light in second cylindrical core222 can be modified, e.g. as explained above by varying the power of theλ2 light transmitted into second cylindrical core 222.

The Two-Core Optical Fiber in Operation

As used herein in this section, optical coupling refers to evanescentwave coupling between cores.

In an exemplary mode of operation of two-core optical fiber 200, a firstinput light signal, comprising a light signal of a first wavelength andhaving a power x₁, is transmitted into first cylindrical core 220 atfirst fiber end 208 via first input port 250. A second input lightsignal, comprising a light signal of the first wavelength and having apower x₂, is substantially simultaneously transmitted into secondcylindrical core 222 at first fiber end 208 via second input port 252.At a same time, a pump light signal of a second wavelength λ₂ and powerx_(p) is transmitted into second cylindrical core 222, e.g. at firstfiber end 208 via control port 262. The pump light signal amplifies thepower of the λ₁ light propagating through second cylindrical core 222.An output light signal is emitted from second cylindrical core 222 atsecond fiber end 210, via second output port 258, and a power y of theoutput light signal may be measured, e.g. by a light sensor (not shown)optically associated with second core 222 at second output port 258. λ₂light emitted from second cylindrical core 222 does not contribute tothe output light signal, and may, for example, be filtered out beforereaching the light sensor, or the sensor may be λ₁ light specific. Itshould be appreciated by the person skilled in the art that additionallyor alternatively another output light signal may be obtained from firstoutput port 256. The λ₁ light transfer rate from first cylindrical core220 to second cylindrical core 222 depends on the powers x₁, x₂, andx_(p), on an amplification rate of the λ₁ light in second core 222, andon the refractive indices of the cores and of the cladding between, onthe distance between the cores, etc. The amplification rate is anincrease in the power of λ₁ light per unit distance along the length ofthe core due to stimulated emission of light. Together with light lossmechanisms, the powers x₁ and x₂ and the λ₁ light transfer ratedetermine the power γ of the output light signal (e.g. from the secondcylindrical core 222). It is thus concluded that optical fiber 200 isconfigured and operable to establish a non-trivial dependency of theoutput light signal on the two input light signals. The above mode ofoperation may be used for example to implement an AND logic gate or anOR logic gate, and to select such functionality of the gates bycontrolling the amplification rate, e.g. by controlling the power of thepump light (the second wavelength λ₂ light), thereby determining—andchanging—the mapping of a set of input light signals onto an outputsignal. For the purpose of the examples provided below, and tofacilitate demonstration, it is assumed that cores 220 and 222 have asame radius, that they are symmetrically located within fiber body 204,and they have a same refractive index. It is also assumed that anylosses during light propagation through the cores are negligible(evanescent wave leakage from one core to another is not considered as aloss, being a transfer of light and as such conserving the total powerin the two cores). It is further assumed that the length L of fiber body204 is such that if only λ₁ light (and no other light, in particular, noλ₂ light) is transmitted into either one of cylindrical cores 220 and222, then a resultant first power of λ₁ light emitted from firstcylindrical core 220 through first output port 256, P₁(z=L), and aresultant second power of λ₁ light emitted from second cylindrical core222 through second output port 258, P₂(z=L), are substantially equal,i.e. the coupling efficiency over the length of the two-core opticalfiber substantially equals one half. It is thus further noted that byselecting an amplification factor of 1 in the second core 222 (namely nonet amplification), the dependency of the output signal power on each ofthe input signal powers, is equal.

To implement the logic gates, a first input bit is encoded in a first λ₁light signal transmitted into first cylindrical core 220 through firstinput port 250, and a second input bit is encoded in a second λ₁ lightsignal transmitted into second cylindrical core 222 through second inputport 252. 0 and 1 are encoded by e.g. a first (substantially zero) powerof the light input and by a second (substantially non-zero) power u ofthe light input, respectively. An output bit is decoded from the powerof λ₁ light emitted from second cylindrical core 222 through output port258. Emitted λ₁ light, having a power smaller than, or substantiallyequal to, a threshold power T>½u, is decoded as 0. Emitted light havinga power greater than T, is decoded as 1. Theoretically, T may beselected to be ½u. In practice, T may be taken to be sufficientlygreater than ½u such that T−½u>Δ whereas Δ is determined by severalfactors, including (a) energy losses in the cores, (b) divergence fromthe theoretical 0.5 value of the rate of transfer of light from thefirst core to the second core along the fiber length, and (c) aresolution of a light sensor used to measure the power of the λ₁ lightemitted from cylindrical core 222. T is also taken to be sufficientlysmaller than u such that u−T>Δ, thereby allowing for satisfactorydiscrimination between ½u and u.

To implement the AND gate no light is transmitted into secondcylindrical core 222 through control port 262. When each of the inputbits equals 0 (i.e. no light is transmitted into either of the cores),no light is emitted from second cylindrical core 222, and the output bittherefore equals 0. When the first input bit equals 0 and the secondinput bit equals 1, no light is transmitted into first cylindrical core220 and light of power u is transmitted into second cylindrical core222. Since the coupling efficiency over L is substantially one half (andsince the cores are substantially lossless), the power of the lightemitted from second cylindrical core 222 substantially equals ½u and theoutput equals 0. Similarly, when the first input bit equals 1 and thesecond input bit equals 0, the output bit equals 0. Finally, when bothinput bits equal 1, λ₁ light of power u is transmitted into both of thecores, and since the cores are substantially lossless and due to theabove-mentioned symmetry of fiber body 204, each of the cores, and inparticular cylindrical core 222, emit light having a power substantiallyequal to u, and the output bit will therefore equal 1.

To implement the OR gate, light is transmitted into second cylindricalcore 222 simultaneously with the encoding of the second bit. When bothinput bits equal 0, the output bit equals 0. When the first input bitequals 0 and the second input bit equals 1, then the λ₂ lighttransmitted into the core amplifies the λ₁ light transmitted into secondcylindrical core 222, and, as a result, λ₁ light having power ν>½u isemitted from second cylindrical core 222 through second output 258. Whenthe first input bit equals 1 and the second input bit equals 0, then theλ₂ light transmitted into the core amplifies the λ₁ light transferredfrom first cylindrical core 220 to second cylindrical core 222, and, asa result, λ₁ light having power ν′>½u is emitted from second cylindricalcore 222 through second output 258. When both input bits equal 1, thenthe λ₂ light transmitted into the core amplifies the λ₁ lighttransmitted into second cylindrical core 222, and, as a result, λ₁ lighthaving power ν″>u is emitted from second cylindrical core 222 throughsecond output 258. By increasing the power of the transmitted λ₂ light,the powers of ν and ν′ may be increased such that ν−T>Δ and ν′−T>Δ(ν″−T>Δ since ν″>u>T+Δ), resulting in the output bit equaling 1 in allinput pairings in which at least one of the inputs equals 1.

By switching the functionality of the two core fiber 200 between an ORgate and an AND gate, a field-programmable gate array (FPGA) may berealized. By employing a similar switching technique to a multi-corefiber as described herein below, an FPGA including tens or hundreds oreven much higher number of gates may be realized.

A Multi-Core Optical Fiber Embodiment

Another embodiment of the invention is schematically depicted in FIGS.3A and 3B. FIG. 3A schematically depicts a multi-core optical fiber(MCF) 400. MCF 400 comprises an MCF body 404, a first MCF end 408, and asecond MCF end 410. MCF body 404 is cylindrical and a longitudinal axis414, coinciding with the z axis, delineates a symmetry axis of thecylinder. First MCF end 408 lies on the xy-plane and second MCF end 410is parallel to first MCF end 408. MCF body 404 houses transmission cores420 (marked as white spots) and amplification cores (marked as blackspots). Each of transmission cores 420, and each of amplification cores430, is cylindrical and extends from first MCF end 408 to second MCF end410 in parallel to longitudinal axis 414. A cladding 440 pervades aninner volume of MCF body 404 submerging the transmission cores 420 andamplification cores 430. Multi-core optical fiber 400, including thecores and the cladding, may be made from materials as is known in theart and as detailed above for two core optical fiber 200. For example,transmission cores 420 and amplification cores 430 may be made of glassor plastic or silica. Amplification cores 430 may be doped for enablinglight amplification as described above. For example, amplification cores430 may be made of silica and doped with Erbium ions. Cladding 440 ismade of a material having refractive index lower than the refractiveindex of transmission cores 420 and the refractive index ofamplification cores 430, e.g. silica.

In some embodiments, not exemplified in the Figures, a transversecross-section of MCF 400, perpendicular to longitudinal axis 414, mayhave a non-circular outline, for example a triangular, square, or evenhexagonal or octagonal or oval (e.g. elliptical) outline. In someembodiments, cores 420 and 430 are arranged in an asymmetrical and/or anon-concentric arrangement relative to longitudinal axis 414. In someembodiments a distribution of dopants in amplification cores 430 may beuniform along the z axis. In other embodiments, the distribution ofdopants may be non-uniform along the length of the amplification core.In some embodiments cladding 440 may be enveloped by a protective jacketor coating. In some embodiments, the periodic structure of hollow tubesmay be interrupted by isolating air holes (either periodic or not) withdiameters within a range between about 10 um to about 4 um. Such airholes may be included within the cladding, either on the circumferenceof the PCF surrounding all the cores, or surrounding specific portion ofthe cores or as part of the functional structure of cores (in anon-surrounding manner). In some embodiments, other modulatingstructures such as gratings could be added within some or all of thecores.

FIG. 3B schematically depicts MCF 400 in a preferred mode of operation.Input ports 450 are associated with all the outer-most cores, preferablyon the first end 408, for inputting light signals at λ₁ wavelength toMCF 400. Output ports 460 are associated with all the inner-most cores,preferably on the second end 410, for outputting light signals (at λ₁wavelength) from MCF 400. It is noted that in the exemplary embodimentof FIG. 3B, all the input ports are associated with amplification coresand all the output ports are associated with transmission cores; howeverit should be understood that this specific allocation of input andoutput ports to types of cores is exemplary and non-limiting. Otherallocations and combination of allocations of input ports and outputports to transmission cores and amplification cores are contemplated andmay be exercised.

For controlling the amplification in the amplification cores, controllight signals at a λ₂ wavelength and at controlled powers (intensities)are transmitted, individually, into the amplification cores throughcontrol ports (not shown in the Figure). Ideally, optical couplingbetween the cores for the λ₂ light is zero, in other words the λ₂ lightmay not transfer from one core to another while propagating along MCF400. Also, ideally, power loss of the λ₂ light along cores isnegligible. Hence, in an ideal MCF, the direction of propagation of theλ₂ light does not affect the amplification in the amplification core andconsequently transmission of control signals into MCF 400 may beaffected through any of first end 408 and second end 410 of MCF 400.Realistic example of λ₂ light propagation in MCF 400, diverging from theideal description above, is detailed further below.

FIG. 4 schematically provides a detailed view of the spatial arrangementof the cores in MCF 400 on the x-y plane. Optical coupling in MCF 400 isrealized through evanescent wave coupling, and hence strongly depends onthe distance between the cores. Straight lines 510 schematically connectadjacent (neighboring) cores, thereby indicating pairs of opticallycoupled cores. It is noted that only some of the optically coupled coresin FIG. 4 are schematically connected by straight lines 510, and itshould be understood that all the pairs of adjacent cores in FIG. 4 areoptically coupled. Each series of optically connected cores (e.g. coresconnected by straight lines 510) forms a sequence through which lightsignals may transfer. Particularly important sequences are those thatconnect an “input” on an outer-most core to an “output” on an inner-mostcore (“input” and “output” relate to cores associated with the inputports and the output ports respectively).

Following the said sequences from “input” to “output”, all the cores inMCF 400 may be grouped into layers 520 a-520 h (denoted in FIG. 4 onlypartially, over a sector of the MCF cross-section). Layer 520 a consistsof all the outer-most cores (associated with input ports 450). The coresin each further layer consist of all the inner cores that are closest tothe cores in the outer layer. Thus layer 520 b consists of all the coresthat are inner and most adjacent to the cores in layer 520 a, layer 520c consists of all the cores that are inner and most adjacent to thecores in layer 520 b, and so on. Layer 520 h thus consists of all theinner-most cores of MCF 400, which are associated with output ports 460.

There is a multitude of sequences (of cores) connecting a particularinput 450 to a particular output 460 in MCF 400. A length of a sequenceis measured by the number of cores comprising the sequence minus 1(namely, the length of a sequence of a neighboring pair of cores is 1).Thus, the shortest sequences between inputs and outputs in MCF 400consist of one core from each layer 520 a-520 h, hence having a lengthof 7.

Cores of MCF 400 are further partitioned into subnets 530 (explicitlysubnets 530 a-530 f), each subnet being encompassed by a dashedtriangle. All the cores in layers 520 a-520 f are included in subnets,whereas the cores in the inner layers 520 g and 520 h are not includedin the subnets.

Groups of cores in MCF 400 are yet further classified into three typesof motifs, wherein a motif is defined as a geometrical arrangement orspatial configuration of a group of cores. A first motif 540 comprisesfour cores: one central core and three surrounding cores. Thesurrounding cores are located on vertices of an equilateral triangle andthe central core is located at the center of the triangle. All the coresin each of the subnets can be grouped into three groups of coresarranged according to the first motif. A second motif 550 comprisesthree cores located on vertices of an isosceles triangle with a vertexangle of 120°. A third motif 560 comprises three cores arranged along astraight line. All the cores in layers 520 g and 520 h are arranged inthe second and third motifs.

As is indicated above, coupling efficiency between a first core (intowhich a light signal is transmitted) to a second neighboring core (intowhich the light signal is transferred from the first core) may varyalong the cores' length. In some embodiments the light efficiency mayhave a maximum at a certain point z (indicating the coupling length),beyond which more light is transferred out of the second core thantransferred into it. MCF 400 is configured to permit an indirecttransfer of λ₁ light, transmitted into the input ports 450, to outputports 460. By indirect transfer of light it is meant that light signalis transferred through a sequence of cores through optical couplingbetween pairs of cores in the sequence. Because a significant transferof light signal within a single pair of adjacent cores occurs along thecoupling length, it is concluded that the total length of a multi-coreoptical fiber of the invention is a function of the series of couplinglengths along the sequence. Preferably, the total length of the fiber ishigher than the coupling length of the first pair in (any of) thesequence and smaller than the total of the coupling lengths, summed overthe shortest sequence of cores from the input to the output. Theshortest sequence of cores from input to output in MCF 400 includes 7pairs of neighboring cores (one less than the numbers of layers 520a-520 h), and the neighboring cores along the sequence are equallydistanced from one another. Hence the length of MCF 400 is less thanabout the coupling length (characterizing neighboring cores in MCF 400)multiplied by 7.

FIGS. 5A-5G schematically depict transfer of light signals alongsequences of cores from input to output, in 7 cross-sections of MCF 400along the z axis. Thus, FIG. 5A schematically depicts a cross-sectionalview of MCF 400 at a distance of about L (equal to the coupling length)from first end 408 of the MCF. Accordingly, FIG. 5A depicts transfer oflight (indicated by arrows) from the outer-most cores in layer 520 a tothe neighboring cores in layer 520 b (the layers are not explicitlyindicated in the Figure). Likewise, FIG. 5B schematically depicts across-sectional view of MCF 400 at a distance from first end 408 of theMCF where coupling efficiency maximizes in the cores in layer 520 bcarrying light that originated in cores of layer 520 a. It should beunderstood that light from the cores in layer 520 b couples also back tothe cores in layer 520 a. However, due to the limited total length ofMCF 400, light signals that diverge from the shortest sequence of coresfrom input to output (namely, light signals that transfer from core tocore along sequences that are different, and hence longer, than theshortest sequence), may not eventually contribute to the output signal.It is thus concluded that MCF 400 is configured and operable toestablish a non-trivial dependency of the output light signals (e.g. inany of output ports 460 a-460 f) on the input light signals. Moreover,it is noted that by selecting an amplification factor of 1 in all theamplification cores 430, each of the output signals is equally dependenton at least eight input signals (associated with eight differentshortest sequences that include the respective output).

Amplification cores 430 are configured such that light having a secondwavelength λ2 propagating in any one of amplification cores 430 isabsorbed in dopant ions to generate excitation of their electrons, therelaxation of which is facilitated by λ1 photons. In the relaxationprocess the dopant ions emit additional λ1 photons with the same phaseas the facilitating λ1 photons, thereby increasing the power of thealready present light of wavelength λ1 therein.

MCF 400 is further configured such that the optical coupling induced bya light signal of wavelength λ2 between two adjacent cores is weakerthan the optical coupling induced by the λ1 light. Transfer of λ2 lightfrom a first amplification core to a second amplification core isgenerally undesired as it may result in a decrease in the amplificationin the first amplification core, and possibly an undesired amplificationof λ1 light within the second amplification core.

Existing technology for providing amplification in optical fibers—e.g.by doped cores as described above—may impose a minimum total length ofthe multi-core fiber. In other words, the total length of the multi-corefiber of the invention may, in some embodiments, be dictated by theamplification per unit length available by current technology. Thus, insuch embodiments, the coupling length (for λ1 light) must be correlatedwith the fibers total length so to maintain a required ratio, asdetailed and explained above, between the coupling length and thefiber's total length. Such establishing of the coupling length may beachieved by properly configuring parameters of the multi-core fiber thataffect the coupling length, for example configuring the distance betweenneighboring cores. It is noted that effective optical lengthening of amulti-core fiber of the invention may also be achieved by reflectingback optical signals into the fiber, by a mirror (or a multitude ofindividual mirrors for each core) at the second end 410 of MCF 400.

According to some embodiments, amplification of light in amplificationcores 430 may involve the use quantum dot lasers.

FIG. 6 schematically depicts a system-on-chip 600 incorporating amulti-core optical fiber of the invention (without sacrificinggenerality of the invention, referred to herein as MCF 400). System onchip 600 comprises a chip body 610, MCF 400, a first Light EmittingDiode (LED) array 620, a second LED array 622, an input coupler 630,light detectors array 640, input connectors 650, output connectors 660and power connectors 670. Input connectors 650, output connectors 660,and power connectors 670 all extend from an inside of chip body 610 toan outside of chip body 610. Input connectors 650 are configured totransmit input signals to first and second LED arrays 620 and 622.Output connectors 660 are configured to receive output signals fromlight detectors array 640. Power connectors 670 are configured toconnect to an external power source (not shown) andto provide power tooperate system 600, particularly LEDs arrays 620 and 622 and lightdetectors array 640. Each LED in first LED array 620 is configured toemit λ1 light. Each LED in second LED array 622 is configured to emit λ2light. System on chip 600 is configured such that light emitted by eachLED in LED arrays 620 and 622 is guided into input coupler 630. Inputcoupler 630 optically couples each LED to a single input port at MCF end408. It is noted though that, in some embodiments, a particular inputport may be coupled both to a λ1 LED (for receiving an input signal) andto a λ2 LED (for receiving a control signal). Light detector array 640is configured such that light emitted by each output port in MCF 400 atsecond MCF end 410 is detected by a corresponding light detector inlight detector array 640. It should be appreciated by the person skilledin the art that embodiments of the invention may include variouscombinations of system 600 integrated in a single chip, for example asystem including a plurality of MCFs arranged in parallel, andalternatively or additionally a plurality of each of the LED arrays 620and 622, the input coupler 630 and the detector array 640, beingassociated with a single MCF or with a plurality of MCFs, according tothe teachings herein.

FIG. 7 schematically depicts a system 680 configured for inputting alarge number of input light signals to a multi-core optical fiber of theinvention. System 680 employs a Spatial Light Modulator (SLM) 682 tobeam shape the wavefront of light so that light in large number ofdesired cores in the multi-core optical fiber is individually initiated.According to some embodiments system 680 comprises a digital micromirrors array device (DMD) 684, which is electronically commandedthrough input connector 686. DMD 684 is configured to spatially andtemporally modulate an incoming uniform light beam 692, therebygenerating in parallel a multitude of input optical signals to beinputted into the multi-core fiber. An imaging setup 690 focuses animage of the DMD active region on the input port of the optical fiber,so that an image of single micro-mirrors from DMD 684 are individuallyprojected on each input port of the fiber. In operation, DMD 684 mayspatially and temporally modulate an incoming uniform light beam 692 soas to project a desired input, comprising a multitude of individualoptical input signals, onto a multitude of input ports of the fiber.Alternatively or additionally, other techniques may be employed togenerate a vast number of individual light signals projected onto an endof a multi-core fiber. According to some embodiments SLM 682 may employfor example a phase only optical mask (e.g. Duadi and Zalevsky in J.Opt. Soc. Am. A, Vol. 27, No. 9, September 2010, p. 2027) for generatingthe required two dimensional (2D) array of input signals with uniformenergy.

The Multi-Channel Optical Module as an Artificial Neural Network

According to some embodiments depicted schematically in FIGS. 8A and 8B,a learning system 800 comprising a multi-channel optical module (MCOM)810 of the invention may be used to implement an Artificial NeuralNetwork (ANN). MCOM 810 comprises a multitude of optically coupledtransmission channels and amplification channels (not explicitly shownin this Figure) as is described and explained herein above. To implementlearning, the learning system 800 is taught or trained to classify setsof data into categories or classes. For example, the system may betasked with classifying a set of passport photo images according towhether an image is of a woman or of a man.

MCOM 810 comprises a data input 812 configured to receive input signalsrepresenting data elements needed to be categorized, and data output 814configured to transmit, as a response to inputting a particular dataelement, an output signal indicating a classification or categorizationof the data element according to a learned rule. Input 812 and output814 are associated with the plurality of optical channels in MCOM 810according to the teachings herein above. MCOM 810 further comprises acontrol input 816 configured to receive control signals, the controlsignals being suitable to control the amplifications of theamplification channels of MCOM 810.

System 800 further comprises a control signal driver 820, functionallyassociated with control input 816 and configured to generate controlsignals suitable to control the amplifications of the amplificationchannels of MCOM 810. A memory module 830, functionally associated withcontrol signal driver 820, is configured to record and deliver tocontrol signal driver 820 a set of selected amplification values,according to which control signal driver 820 generates the requiredcontrol signals. A processor 840 is configured to perform a learningalgorithm so as to implement system 800 with a desired learning rule.Processor 840 is functionally associated with output 814 of MCOM 810 toreceive output signals therefrom, and functionally associated withmemory 830 to provide a set of selected amplification values.

For use, each data element in a data set that need to be classified maybe represented by a string of bits. A set of strings of bits may beencoded in substantially distinct sets of powers of input light signalsinputted to the MCOM 810. As a non-limiting example, in a version ofsupervised learning, a training set may be selected. The training set isa subset of the data, such that each data element in the training set iscategorized—for example a subset of passport photo images wherein thegender of the person in the image is pre-categorized as “male” or“female”. Each data element in the training set is encoded in a set ofinput powers. Also, each category is encoded in a distinct output set ofoutput powers. Then a set of control signals (e.g. pump light powers)may be found, in the process of “learning”, such as to map correctly thelearning set onto the required output set. In other words, a single setof amplification values is found such that each data element from thetraining set, when inputted to system, generates an output thatindicates the correct category of the input. For example, for each inputin the training set that relates to an image photo, the output indicateseither “male” or “female”, in agreement with the pre-categorization ofthe image photos.

The required amplification values may be found in a (non-limiting)exemplary process as follow: a first set of amplification values isselected by processor 840 e.g. at random, and provided to MCOM 810. Afollowing set of steps is then performed: One at a time, each encodeddata is transmitted into input 812, and a set of control signalsassociated with the selected amplification values is simultaneouslytransmitted into control input 816. Resultant output signals emittedfrom output 814 are measured and recorded by processor 840. Once all ofthe encoded data have been transmitted and resultant output signals havebeen recorded, the learning algorithm is implemented by processor 840 soas to generate a new set of amplification values. For example, amagnitude of an error, i.e. a cost function quantifying how ‘far’ onaverage the resultant sets of output powers are from the correct sets ofoutput powers, may be computed. If the error magnitude is above adesired threshold, an algorithm may be used to compute from the outputsignals and the current amplification signals, a new set ofamplification signals to be used in a next step. The set of steps isrepeated until the error magnitude is sufficiently small and a desiredlevel of classification is achieved.

Once a desired single set of amplification values is found such that theset allows for correct classification of the whole training set, thelearning phase of system 800 is complete, and classification may beimplemented by system 800 a schematically depicted in FIG. 8B. System800 a is different from system 800 by not having processor 840 which isnot necessary (to the extent of implementing the learning algorithm).Memory 830 provides the single set of amplification values that wasfound during the learning phase, which set is used for classifying theentire input data set. According to some embodiments, learning instancesmay still apply intermittently during normal use (hence system 800 ofFIG. 8A may be used also after completing the first learning phase), torefine the selected amplification values determining the classification.

According to some non-limiting embodiments, MCOM 810 may be realized bya multi-core optical fiber, comprising a multitude of optically coupledtransmission cores and amplification cores according to the teachingsherein. In some embodiments a multi-core optical fiber of the inventionmay include hundreds of thousands of cores in line with currentstate-of-the-art fiber technology. Such a high number of cores may allowfor implementation of complex and cumbersome computations and tasks.

Simulations of Multi-Core Optical Fiber in Operation

To demonstrate learning, an optical simulation of light propagation in amulti-core optical fiber of the invention was performed. The simulatedmulti-core optical fiber has a core arrangement on the x-y cross-sectionthereof similar to that of MCF 400, namely as schematically described inFIGS. 3-5 above. Hence the simulated multi-core optical fiber isreferred to herein below as MCF 400, without wishing to limit thegenerality of the invention. For the sake of the simulation, specificvalues were assigned to some physical parameters characterizing MCF 400.The length of MCF body 404 was set to equal 9 mm. The pitch between alladjacent (neighboring) cores was set to 9 μm. The core diameter is 8pnm. Transmission cores 420 and amplification cores 430 were assigned arefractive index of 1.52 and cladding 440 was assigned a refractiveindex of 1.48. For these values a numerical aperture of about 0.35 and acritical angle of about 20.27° are obtained. Amplification cores wereassigned an amplification rate of 850 dB/m. That is to say,amplification by a factor of approximately 1.216 per mm. A wavelength ofinput light signals, λ₁, was taken to equal 1,550 nm and a wavelength ofpump light signals, λ₂, was taken to equal 980 nm. Both input and pumplight signals were assigned a Gaussian intensity profile in the x and ycoordinates. Using the assigned specific values, coupled wave equationsfor a propagation of light in a multi-core optical fiber werenumerically solved using RSoft simulation software (Synopsis, Calif.,USA) in conjunction with self-written MATLAB code.

FIGS. 9A-9D present a comparison of light transfer rates of light havinga wavelength λ₁=1,550 nm and of light having a wavelength λ₂=980 nm inMCF 400. In the examples shown here, λ₁ light and λ₂ light are inputted(separately) into the cores in the outer layer (layer 520 a in FIG. 3B)of MCF 400. FIGS. 9A and 9B schematically show light intensity (ofλ₁=1,550 nm light) in cores along a cross-section of MCF 400 at z, y,x=14.5 μm and along a cross-section at z, y, x=18 μm, respectively. FIG.9E presents a power scale, wherein the level of power is represented ona gray-level scale. Power values of light signals is displayed inarbitrary units (a.u.)—a linear scale where maximal input power isnormalized to 1. The figures show qualitatively the gradual increase anddecrease of light intensity in each core, as λ₁ light transfers viaoptically coupled cores, from the outer cores to the inner cores. It isnoted that the length of MCF 400 is closely related to the couplinglength of neighboring cores and to the total number of cores in thesequence of cores from input to output, so that MCF 400 length is tunedso that the output light signal is that which transferred via theshortest sequence of cores in the fiber. It is further noted that somelight couples “back” from inner cores to outer cores, however, as ismentioned above, due to the finite length of MCF 400, such light signalsmay not affect significantly the output in the inner cores.

FIGS. 9C and 9D schematically show the transfer of λ₂=980 nm light alongsimilar cross-sectional planes of MCF 400, namely at z, y, x=14.5 μm andz, y, x=18 μm, respectively. The figures show that the coupling lengthof the 12 light is much greater than the coupling length of the λ₁light, and is even longer than the total length of the fiber. Since onlytransmission cores neighbor amplification cores in MCF 400, it isconcluded that amplification selectivity is maintained, namely no λ₂light may transfer from one amplification core to another amplificationcore within the length of the fiber.

FIGS. 9F and 9G depict the power of light signals of wavelengths λ₁ andλ₂, respectively, in each of the cores at four cross-sections of MCF 400along the z axis, namely at z=0 mm (i.e. at first MCF end 408, showntopmost), z=3 mm, z=6 mm and z=9 mm (i.e. at second MCF end 410). InFIG. 9F, at z=0 mm, input light signals of wavelength λ₁=1,550 and equalpower are transmitted into all the cores in the first (outer-most) layerof cores, whereas no light is transmitted into any of the other cores.At z=3 mm, most of the 1,550 nm light signal is transferred from thefirst layer of cores to the second and third layer of cores, and thepower in each core in the third layer at z=3 mm is approximately 75% ofthe power in each core in the second layer at z=3 mm. At z=6 mm, most ofthe 1,550 nm light signal is transferred to the fifth layer of cores. Atz=9 mm, most of the 1,550 nm light signal is transferred to the last andeighth layer of cores, i.e. to the output.

In FIG. 9G, at z=0 mm, input light signals of wavelength λ₂=980 nm andequal power are transmitted into all the cores in the first layer,whereas no light is transmitted into any of the other cores. At z=3 mm,most of the 980 nm light is still mostly concentrated in the cores ofthe first layer. Likewise, at z=6 mm, most of the 980 nm light is stillmostly concentrated in the cores of the first layer with a noticeableamount having been transferred to the second layer of cores. The powerin each core in the second layer at z=6 mm is approximately 67% of thepower in each core in the first layer at z=6 mm (note that light istransferred to each core in the second layer from two respective coresin the first layer, namely there are twice the number of cores in thefirst layer relative to the second layer). At z=9 mm, most of the 980 nmlight has transferred from the first layer of cores and peaks in thecores of the second layer: the power in each core in the first layer atz=9 mm is approximately 67% of the power in each core in the secondlayer at z=9 mm. The power in each core in the third layer equalsapproximately 25% and less than the power in each core in the secondlayer. The power in each core in the fourth layer and beyond equalsapproximately 10% and less than the power in each core in the secondlayer. Thus comparison shows that the 1,550 nm light signal has a lighttransfer rate more than seven times higher than the light transfer rateof the 980 nm light signal.

FIGS. 10A-10F present results of a simulation demonstratingclassification capabilities of an MCF 400. In the simulation MCF 400 wastasked with distinguishing (i.e. singling out) a targeted string00111100 from amongst a set of all possible eight bit strings comprisingfour “zeros” and four “ones”. Each bit was encoded as an input lightsignal of 1,550 nm wavelength transmitted into a corresponding input ofMCF 400. 0 was encoded as an input light signal of zero power (i.e. nosignal is transmitted) and 1 was encoded as an input light signal of apre-determined non-zero power. FIG. 10A schematically depicts thespatial arrangement of the cores in MCF 400. For the said classificationtask, the subnets 530 a-530 f are grouped to couples, couple 710comprising subnets 530 a and 530 b, couple 712 comprising subnets 530 cand 530 d and couple 714 comprising subnets 530 e and 530 f. It is notedthat each couple comprises 8 input bits, allowing to input an eight-bitstring to a single couple. Each couple further corresponds to oneoutput, namely couple 710 corresponds to output 460 b, couple 712corresponds to output 460 e and couple 714 corresponds to output 460 f.

A category of a string (i.e. whether the string is the targeted stringor not) was encoded in an output light power of a single output. Anoutput power higher than a threshold power, classified the pattern asthe targeted string, while an output power lower than the thresholdpower classified the string as different from the targeted string.

In the simulation, the targeted string was inputted to couple 710,whereas encodings of control strings 11001001 and 10011001 weretransmitted into couples 712 and 714, respectively. FIG. 10Aschematically depicts the amplification pattern that was selected todistinguish between the targeted string and the two control strings.FIG. 10A shows the spatial arrangement of non-amplified cores 720(functioning substantially as transmission cores) and amplified cores730, in MCF 400. In other words, amplified cores consist ofamplification cores that are actually pumped with pump light signals (at980 nm).

FIG. 10B shows results of a simulation wherein an encoding of thetargeted string was transmitted into the input of couple 710 andencodings of the control strings 11001001 and 10011001 were transmittedinto the input of couples 712 and 714, respectively. It is noted thatthe power output of output 460 b is markedly higher than the outputpowers of output 460 d and of output 460 f. It is concluded that theselected amplification pattern succeeds is distinguishing the targetedstring from the control strings.

FIGS. 10C and 10D show results of a first control simulation and asecond control simulation wherein the same patterns as in the simulationof FIG. 10B were encoded and transmitted, but the amplification patternwas different from the pattern shown in FIG. 10A. In the simulation ofFIG. 10C, all the amplification cores (as displayed in FIG. 4) wereactually used for amplification; whereas in the simulation of FIG. 10D,none of the amplification cores were used for amplification. In thefirst control simulation (FIG. 10C) the output signals all had an equaland high power. In the second control simulation (FIG. 10D) the outputsignals all had an equal and low power. It is thus concluded that theamplification patterns that are tested in the simulations of FIGS. 10Cand 10D cannot distinguish the targeted string from the control strings.

FIG. 10E shows a comparison of output light signals powers for each pumplight power profiles, i.e. the optimal profile of FIG. 10B, the equaland high power profile of FIG. 10C, and the equal and low power profileof FIG. 10D. The OUTPUT numbers (1, 2, 3, . . . 6) denoted on the x axisrefer to output ports 460 a, 460 b 460 c, . . . , 460 f, respectively.The control simulations demonstrate a specificity of amplification powerprofiles, i.e. not all profiles can be used for a same task.

FIG. 10F shows results of a simulation wherein all possible eight bitstrings comprising four zeros and four ones were encoded and transmittedinto MCF 400 wherein the amplification pattern was selected to be the“optimal” pattern as depicted in FIG. 10A. A horizontal axis representsa correlation coefficient of an encoded string with the targeted string.A vertical axis represents the output light signal power (of output 460b). The output light signal power is seen to grow larger the closer anencoded string is to the targeted string (have a higher coefficient ofcorrelation), thereby demonstrating classification capabilities of MCF400.

FIG. 11A presents results of a simulation demonstrating classificationusing close to realistic amplification levels. In the simulationamplification cores were assigned an amplification level of 41 dB/m,approximately twenty times weaker than the amplification level inpreceding the simulations described above. To compensate for the weakeramplification level, MCF body 404 was assigned a length of 110 mm, and apitch between all adjacent cores was set to 14 μm. The core diameter is8 μm. While output signals were overall weaker as compared to outputsignals in FIG. 10b , reproduced here for comparison as FIG. 11B, anoutput signal emitted from first core 460 b had significantly more powerthan any other output signal, meaning that all three bit strings werecorrectly categorized.

Numerical simulations further indicate the robustness (stability) of theclassification functionalities of MCF 400 under typical optical-fibermanufacturing defects and implementation-related imperfections.Specifically, simulations were carried out to test the robustness under:a stress-like warping at a random angle in the x-y plane (i.e.perpendicularly to longitudinal axis 414), changes to the length of MCF400, global (as opposed to local) changes to the refractive indices ofthe core and the cladding, and tilting of a beam angle of an input lightsignal transmitted into a core. The above-mentioned warping could arise,for example, during the pulling of MCF 400, due to an unevenly appliedpressure along the length of the fiber, resulting, for example, in thedistances between cores being uneven across the x-y plane. Further, thedistance between a pair of cores could change as a function of the zcoordinate (namely along the length of MCF 400).

Manufacturing defects, such as over-doping or under-doping ofamplification cores 430 were not simulated since such deformations canpotentially be compensated for by modifying the intensities of the pumplight signals.

In the robustness simulations, MCF 400 was tasked with singling out thesame targeted pattern (i.e. 00111100) as in the numerical simulations ofFIGS. 10A-10F. The robustness simulations were carried out using theinput light signals and pump-light signals of FIG. 10B. The simulationsdemonstrated stability under a variance as high as 5% per meter in thewarping (whereas state-of-the-art fabrication allows for variances ofabout 1-2% per meter), even when the length of MCF 400 and therefractive indices of the core and cladding were modified by as much as5%. That is to say, the ratios of the powers of the output signals fromoutput cores 460 a, 4650 c and 460 f remained similar to those of theideal case (shown in FIG. 10B), even though the powers werecomparatively weaker. Further, the robustness simulations demonstratedstability even when the input light signals were made to enter the coresat an angle of up to 8° relative to longitudinal axis 414 (rather thanentering in parallel to longitudinal axis 414 as in the numericalsimulations of FIGS. 10A-10F).

A Photonic Crystal Fiber Embodiment

PCFs form a subclass of micro-structured optical fibers in which thestructural properties of the fiber may contribute to the confinement oflight regardless of differences in refractive indices. PCFs exhibit aperiodic structure on a transverse cross-section of the fiber,perpendicular to an axis extending along a length of the fiber. Allclasses of PCFs comprise a periodic array of hollow tubes, air-holes.The periodic array gives rise to two-dimensional photonic bandgaps—ranges in two-dimensional virtual space of frequency and axialpropagation constant component, for which the cladding does not permitlight propagation. In all PCFs the cores which confine light arelocations where periodicity breaks, either by omission of an air hole(resulting in a solid core) or by insertion of a hole with a largerradii than the air-holes (resulting in a hollow core).

Another embodiment of the invention described herein comprises ahole-assisted photonic crystal fiber (PCF) as is schematically depictedin FIG. 12. FIG. 12 depicts a transverse cross-section of a PCF 1300.PCF 1300 comprises a body 1304 having a transverse cross-section in ashape of a hexagon and having two ends (not shown) parallel to the planeof the Figure. Hexagonal body 1304 comprises PCF transmission cores 1310and PCF amplification cores 1320 extending from one end of body 1304 tothe other end, and a cladding 1340 submerging the cores. PCF cladding1340 comprises a periodic array of hollow tubes 1344, each tubeextending from one end of hexagonal body 1304 to the other end.

PCF transmission cores 1310 and PCF amplification cores 1320 arearranged in a substantially same geometry as the geometry oftransmission cores 420 and amplification cores 430 in MCF 400. PCFtransmission cores 1310 and PCF amplification cores 1320 are configuredto permit a propagation of light having a first wavelength μ₁therethrough. PCF amplification cores 1320 are doped and are configuredto amplify μ₁ light propagating therethrough by stimulated emission ofdopants excited by light having a second wavelength λ₂ transmittedtherein. PCF cladding 1340 is configured such that μ₁ light and μ₂ lightincident on cladding 1340 can penetrate therein only as evanescentwaves. PCF transmission cores 1310 and PCF amplification cores 1320 arefurther configured to allow a transfer of μ₁ light between adjacentcores at a light transfer rate higher than light transfer rate for μ₂light between adjacent cores.

In an exemplary mode of operation, PCF 1300 is operated in asubstantially same way as MCF 400 as described above, with PCFtransmission 1310 cores, PCF amplification cores 1320, and PCF cladding1340 function analogically to transmission cores 420, amplificationcores 430, and cladding 440, respectively. It is thus concluded that PCF1300 is configured and operable to establish a non-trivial dependency ofthe output light signals (e.g. in any of outputs in the inner-most layerof cores in FIG. 12) on the input light signals (e.g. in the outer-mostlayer of cores in FIG. 12).

In some embodiments, not exemplified in the Figures, a transversecross-section of PCF 1300, may be for example triangular, square, oreven circular. In some embodiments PCF transmission and amplificationcores 1310 and 1320 are arranged in an asymmetrical and/or anon-concentric manner. In some embodiments PCF transmission cores 1310and PCF amplification cores 1320 may be made, for example, of plastic.In some embodiments PCF amplification cores 1320 may be doped, forexample, with Germanium ions. In some embodiments a distribution ofdopants in PCF amplification cores 1320 may be uniform. Still, in otherembodiments, the distribution of dopants may depend on a location alonga length of an amplification core. In some embodiments PCF cladding 1340may be enveloped by a protective jacket or coating. According to someembodiments, amplification of light in PCF amplification cores 1320 mayinvolve the use quantum dot lasers.

A Photonic Crystal Slab Embodiment

Another embodiment of the invention described herein comprises aphotonic crystal slab 1500 schematically depicted in FIG. 13. Photoniccrystal slab 1500 comprises a shaped (e.g. rectangular) body 1504. Body1504 comprises a first face 1508 and a second face (not shown) oppositeto the first face. First face 1508 lies on the xz-plane. Rectangularbody 1504 is structured as a periodic array 1516 of hollow tubes 1518.Each of the hollow tubes forms a hole extending from first face 1508 tothe second face along a cylindrical symmetry axis of the tube parallelto the y axis. Photonic crystal slab 1500 comprises optical channels1520 structured as elongated narrow, typically straight tunnels throughthe periodic array 1516, thus forming line defects in the periodicstructure of body 1504 thereby being configured to allow for efficientpropagation of light particularly at selective wavelengths or in awavelengths range therethrough. Optical channels 1520 may be formed ashollow tunnels through the periodic array 1516, or as tunnels filledwith optically transparent material, as is known in the art of photoniccrystals.

At least some of the optical channels 1520 in photonic crystal slab 1500are interconnected to one another to form a net 1530 of interconnected,optically coupled optical channels. Optical channels 1520 merge andthereby optically couple in optical junctions 1532, junction 1532 beingconfigured to combine powers of light signals from at least two opticalchannels merging into the junction, into a combined light signal in oneor more outgoing optical channels. According to some embodiments thecombination of powers of incoming light signals into junction 1680 maybe a linear combination. According to some embodiments the linearcombination may be a direct sum of the powers. Optical channels 1520 areinterconnected so that net 1530 extends continuously from an input face1534 to an opposite output face 1536 of rectangular body 1504. Net 1530comprises input ports 1540 (or “inputs”) on input face 1534, configuredto allow transmission of a light signal therethrough into opticalchannels 1520 of net 1530. Likewise, net 1530 comprises output ports1550 (or “outputs”) on output face 1536, configured to allow emission ofa light signal therethrough from optical channels 1520 of net 1530. Eachexposed end of optical channels 1520 on input face 1534 and on outputface 1536 may function as an input port and an output port,respectively. It is noted however that in photonic crystal 1500, anyexposed end of an optical channel 1520 on the slabs edge may bearbitrarily used as an input or as an output (or even as both), forexample light signals may be inputted to net 1530 through the outputports 1550 and outputted through the input ports 1540. It isnevertheless concluded that propagation of light signals through net1530 establishes a multitude of light paths, each light path beingdefined by a single starting point and a single end point andinterconnecting optical channels through which light may propagate. Suchlight paths generally comprise a sequence of junctions 1532interconnected by optical channels. A length of a sequence in net 1530is thus defined by the number of junctions 1532 along the light path. Itis noted that the shortest sequences between inputs and outputs in net1530 is of length 3.

Net 1530 is generally configured to allow for light having a suitablewavelength to propagate therethrough, being prevented from escaping intoperiodic array 1516, or into the air above first face 1508 and below thesecond face, due to refraction indices differences. Accordingly, net1530 is configured to optically indirectly couple inputs 1540 withoutputs 1550 through sequences of interconnected optical channels 1520thereof. Thus, light signals inputted to photonic crystal 1500 throughthe multitude of inputs 1540 propagate through net 1530. According tosome embodiments, light propagation along the general direction of the zaxis, namely along the general direction from input face 1534 towardsoutput face 1536, is preferred. Light signals propagating throughoptical channels 1520 that interconnect, combine together to generate aresulting light signals having a combined power of the powers of thecombined signals. Typically, the power of the resulting signal is thesum of powers of the combined signals. In some embodiments the resultingpower is a linear combination of the powers of the combined signals,namely the resulting power equals a sum of combined powers, eachmultiplied by a respective constant. It is concluded that photoniccrystal 1500 is configured and operable to establish a non-trivialdependency of the output light signals in outputs 1550 on the inputlight signals in inputs 1540. Moreover, it is noted that by selectingsuitable amplification factors at least in some amplification channels,each of the output signals may be equally dependent on at least twoinput signals. At least one—and preferably more than one—of opticalchannels 1520 are amplification channels 1570 configured to controllablyamplify a light signal propagating therethrough. According to someembodiments, amplification channels 1570 comprise doped segments 1572,doped with excitable ions such as Erbium ions or Germanium ions. Thus,photonic crystal slab 1500 is configured such that light of a firstwavelength ν₁ may propagate through net 1530, whereas light of a secondwavelength ν₂ projected onto any of doped segments 1572 may generatecontrolled stimulated emission of ν₁ light propagating therethroughthereby controllably amplifying the ν₁ light propagating through therespective optical channel. For use, ν₂ light may be independentlyprojected on the doped segments 1572, e.g. by respective light sources1580, wherein each light source generates a light beam 1582 producing alocal light spot 1584 on a respective doped segment 1572. By selectivelycontrolling the power of the individual light spots 1584, selectivecontrolled amplification of ν₁ light along the amplification channels1570 may be effected.

In some modes of operation of photonic crystal 1500, input light signalsare selectively transmitted into each of inputs 1540, and a set ofoutput light signals is emitted from outputs 1550. The input lightsignals and the output light signals are of wavelength ν₁. The power ofthe input light signals transmitted into any one of inputs 1540 isindividually controllable. The ν₁ light signals propagating throughconverging (combining) optical channels 1520 combine together asexplained above. ν₁ light propagating through amplification channels1570 (comprising doped segment 1572) may be controllably amplified bycontrollably varying the power of ν₂ light projected on the dopedsegment. Thus, photonic crystal slab 1500 allows to controllably mapsets of input light signals onto sets of output light signals.

In some embodiments optical channels 1520 are embedded with quantumwells. According to some embodiments, amplification of light in theamplification channels 1570 may involve the use quantum dot lasers.

Photonic crystal slab 1500 may implement an ANN wherein synapses areidentified with optical channels 1520, and neurons are identified withconvergence or confluences thereof. The latter identification ofsynapses with optical channels 1520 may be made even for opticalchannels that do not amplify, in which case a corresponding synapse maynot amplify.

A 3D Photonic Crystal Embodiment

New techniques have recently been demonstrated for generating 3D ordereddefects (e.g. line defects) in 3D photonic crystals. For example, Rinneet al (Nature Photon. 2, 52-56 (2008)) suggest a four-step method,comprising assembling a 3D ordered planar silica opal on a siliconsubstrate; generating well-defined polymer defects with submicrometerscale resolution by scanning a focused laser beam through the opalimmersed in a photosensitive monomer; filling interstitials betweensilica particles with amorphous silicon, using a low-temperaturechemical-vapour-deposition process; and removing the silica-spheretemplates and micropatterned polymer defects by wet etching andcalcination, respectively—resulting in a silicon inverse opal withincorporated air-core defects. Such methods allow for incorporation intothe 3D photonic crystals of optically active materials such as quantumdots, nonlinear materials or liquid crystals, to provide on-demand lightmanipulation, e.g. light amplification.

FIG. 14 schematically depicts an embodiment of a 3D photonic crystal1600 according to an aspect of the invention. 3D photonic crystal 1600comprises a body 1604 comprising a three-dimensional periodic dielectricstructure as is known in the art of 3D photonic crystals. 3D photoniccrystal 1600 further comprises transmission channels 1610 andamplification channels 1620. Transmission channels 1610 comprisetunnels, i.e. line defects through body 1604 configured to allow lightpropagation therethrough. The line defects may be hollow or may befilled with solid transparent material. Amplification channels 1620 areconfigured to allow light propagation therethrough and furtherconfigured to allow to controllably amplify such propagating light.According to some embodiments amplification channels 1620 comprise linedefects through body 1604, filled with solid, substantially transparentmaterial suitable to be used in transmission channels 1610, wherein thematerial is further doped with ions such as Erbium or Germanium ions,suitable to be excited by a λ_(\2) light to amplify λ₁ light by way ofstimulated emission as described above. Some of the transmissionchannels and the amplification channels are optically associated withinput ports 1640 and with output ports 1650, having exposed ends onfaces of body 1604, thereby allowing the transmission of input lightsignals (designated as λ₁ light) into the channels and emission ofoutput light signals (being also λ₁ light) from the channels. Accordingto some embodiments amplification channels 1620 are further associatedwith control ports 1660, configured to allow transmission of controlsignal into the amplification channels, a control signal beingconfigured to determine an amplification factor in the associatedamplification channel. According to some embodiments, control signalsmay comprise λ₂ light transmitted into the amplification channel throughan exposed end thereof on a face of body 1604, the power (intensity) ofthe λ₂ light determining the amplification factor in the amplificationchannel.

At least some of the optical channels (namely transmission channels 1610and amplification channels 1620) optically couple by converging andmerging in optical junctions 1680 within body 1604. Optical junction1680 is configured to combine light powers of at least two opticalchannels merging into the junction into a combined light signal in oneor more outgoing optical channels. According to some embodiments thecombination of powers of incoming light signals into junction 1680 maybe a linear combination. According to some embodiments the linearcombination may be a direct sum of the powers. The interconnectedoptical channels thus form a net 1690 of interconnected channels,indirectly coupling input ports 1640 with output ports 1650.

In some modes of operation of 3D photonic crystal 1600, input lightsignals are selectively transmitted into each of inputs 1640, and a setof output light signals is emitted from outputs 1650. The input lightsignals and the output light signals are of wavelength ν₁. The power ofthe input light signals transmitted into any one of inputs 1640 isindividually controllable. The ν₁ light signals propagating throughconverging (combining) transmission channels 1610 and amplificationchannels 1620 combine together in junctions 1680 as explained above. ν₁light propagating through amplification channels 1620 may becontrollably amplified, e.g. by controllably varying the power of ν₂light individually transmitted into the amplification channels. It isconcluded that 3D photonic crystal 1600 is configured and operable toestablish a non-trivial dependency of the output light signals inoutputs 1650 on the input light signals in inputs 1640. Moreover, it isnoted that by selecting suitable amplification factors at least in someamplification channels, the output signal may be equally dependent onseveral input signals. Thus, 3D photonic crystal 1600 allows tocontrollably map sets of input light signals onto sets of output lightsignals.

Thus, according to an aspect of some embodiments, there is provided anintegrated multi-channel optical module (e.g. 100 in FIG. 1; 200 inFIGS. 2A-2B; 400 in FIG. 3A, FIG. 6, and FIG. 7; 810 in FIGS. 8A-8B;1300 in FIG. 12; 1500 in FIG. 13; 1600 in FIG. 14) for controllablymapping sets of input light signals onto sets of output light signals.The optical module comprises:

-   -   At least two optical channels (e.g. 110, 120 in FIG. 1; 220, 222        in FIGS. 2A-2B; 420, 430 in FIGS. 3A-5G; 720, 730 in FIG. 10A;        1310, 1320 in FIG. 12; 1520 in FIG. 13; 1610, 1620 in FIG. 14)        configured to allow directional propagation of light therein,        wherein at least one of the optical channels is an amplification        channel (e.g. 120; 222; 430; 730; 1320; 1570; 1620) configured        to allow amplification of light propagating therein by a        controllable amplification factor.    -   At least two input ports (e.g. 130; 250, 252 in FIG. 2B; 450 in        FIGS. 3B-5G and in FIG. 10A; 1540; 1640), individually        associated with the at least two optical channels, and        configured to allow transmission of input light signals into the        optical channels.    -   At least one output port (e.g. 140; 256, 258 in FIG. 2B; 460 in        FIGS. 3B-5G and in FIG. 10A; 1550; 1650) optically associated        with one of the optical channels, and configured to allow        emission of an output light signal from the one optical channel.        At least one control port (e.g. 122; 262 in FIG. 2B; 1660)        functionally associated with the amplification channel and        configured to allow inputting a control signal to the        amplification channel to determine the amplification factor.        The optical channels are optically coupled so that a power of an        output light signal emitted from the output port is a function        of powers of the at least two input light signals transmitted        through the at least two input ports.

In some embodiments, the optical module comprises at least two outputports (e.g. output ports 140 associated with channels 160 a 3 and 160 b3, respectively; 256, 258; 460 a-460 f in FIGS. 4 and 460 b, 460 d, and460 f in FIG. 10A) optically associated with the at least two opticalchannels, respectively.

In some embodiments, the optical module comprises M (e.g. 256 and 258;the six output ports 460 a-460 f depicted in FIG. 4) output portsoptically associated with M of the at least two optical channels, and Ninput ports (e.g. 250 and 252; the 24 input ports 450 depicted in FIG.4) optically associated with N of the at least two optical channels,wherein 2<M<N.

In some embodiments, the optical module is a multi-core optical module(e.g. 200; 400; 1300) comprising at least two cores (e.g. 220, 222; 420,430; 720, 730; 1310, 1320) configured to allow directional propagationof light therein. At least one of the cores is an amplification core(e.g. 222; 430; 730; 1320) configured to amplify a λ1 light—being lightat a first wavelength λ1 propagating therethrough—by a controllableamplification factor determined by a power of a λ2 light—being light ata second wavelength λ2—propagating therethrough simultaneously with theλ₁ light. The input ports, output ports and control ports compriseexposed ends (e.g. at fiber ends 208 and 210 in FIGS. 2A-2B; at MCF ends408 and 410 in FIG. 3A) of the at least two cores, and wherein the atleast two cores are optically coupled through evanescent wave coupling.

In some embodiments, the amplification core (e.g. 222; 430; 730; 1320)is doped with ions excitable by the λ₂ light and spontaneously emittingupon relaxation the λ₁ light.

In some embodiments, the multi-core optical module is a multi-coreoptical fiber (e.g. 200; 400).

In some embodiments, the multi-core optical module is a multi-corephotonic crystal (e.g. 1300).

In some embodiments, the λ₂ light has a wavelength of about 980 nm andthe λ₁ light has a wavelength of about 1550 nm.

In some embodiments, the optical module is a photonic crystal (e.g. 1500in FIG. 13; 1600 in FIG. 14). The photonic crystal comprises a body(e.g. 1504; 1604) bounded by faces (e.g. 1508, 1534, 1536), a periodicstructure (e.g. 1516) of a dielectric material, and optical channels(e.g. 1520; 1610, 1620) defined by line defects in the periodicstructure formed as tunnels therethrough. The optical channels compriseamplification channels (e.g. 1570; 1620) configured to controllablyamplify a light signal propagating therethrough, wherein the opticalchannels merge in junctions (e.g. 1532; 1680), thereby opticallycoupling and forming a net (e.g. 1530; 1690) extending continuously inbetween the faces. The net comprises at least two input ports on thefaces (e.g. 1540; 1640), configured to enable transmission of inputlight signals to at least two optical channels of the net, and at leastone output port (e.g. 1550; 1650) on the faces enabling to emit anoutput light signal from the optical channel of the net.

In some embodiments (e.g. 1500), the body is a slab, and the periodicstructure of dielectric material comprises an array of hollow tubes(e.g. 1518) extending between two faces of the slab, being therebyperiodic in two dimensions.

In some embodiments (e.g. 1600), the periodic structure of dielectricmaterial is periodic in 3 dimensions and the photonic crystal is a 3Dphotonic crystal.

According to an aspect of some embodiments, there is provided an opticalcomputation device (e.g. 600 in FIG. 6). The optical computation devicecomprises:

-   -   The optical module (e.g. 100, 200, 400, 810, 1300, 1500, 1600).    -   An array of controllable light sources (e.g. 620) selectively        optically associated (e.g. via input coupler 630) with the input        ports.    -   Light detectors (e.g. 640) selectively optically associated with        the output ports.    -   A control signals interface (e.g. 622) functionally associated        (e.g. via input coupler 630) with the control ports.    -   A controller functionally associated with the light sources,        light detectors and control signals interface.

The optical computation device is configured to produce a calculation byinputting input signals (e.g. via first LED array 620) and controlsignals (e.g. via second LED array 622) into the optical module andobtaining output signals therefrom. The output signals are a function ofthe input signals, the function being determined by the control signals.

In some embodiments, the light sources comprise a Spatial LightModulator (SLM) (e.g. 682 in FIG. 7) for generating a multitude ofcontrolled light beams individually optically associated with the inputports, respectively.

In some embodiments, the SLM is a Digital micro Mirrors array Device(DMD) (e.g. 684 in FIG. 7).

According to an aspect of some embodiments, there is provided anartificial neural network (e.g. 800 in FIG. 8A) comprising the opticalcomputation device (e.g. 600 in FIG. 6) and a processor (e.g. 840)functionally associated with a memory (e.g. 830) and with the controller(e.g. 820) and configured to implement a learning algorithm.

According to an aspect of some embodiments, there is provided a methodof performing a calculation. The method comprises:

-   -   Providing a multi-core optical fiber of a length L (e.g. 200 in        FIGS. 2A-2B; 400 in FIGS. 3A-3B, FIG. 6, and FIG. 7; 1300 in        FIG. 12) and comprising a plurality of cores (e.g. 220, 222 in        FIGS. 2A-2B; 420, 430 in FIGS. 3A-5G; 720, 730 in FIG. 10A;        1310, 1320 in FIG. 12) configured to enable directional light        propagation therein along the core. The optical fiber is        configured to enable evanescent wave coupling between        neighboring cores with a coupling length that is shorter than        twice the length L at least for light signals having a first        wavelength λ1 and wherein one or more of the cores are        amplification cores (e.g. 222; 430; 730; 1320) being configured        to amplify the λ1 light according to a power of a control light        signal having a second wavelength λ2 propagating therethrough.    -   Transmitting input light signals having selected individual        powers and the first wavelength λ1 into a plurality of cores of        the multi-core optical fiber.    -   Obtaining output light signals emitted from one or more of the        cores of the multi-core optical fiber, the powers of the output        light signals being a function of the powers of the input light        signals.    -   Transmitting control light signals having selected individual        powers and the second wavelength λ2 into one or more of the        amplification cores of the multi-core optical fiber, thereby        defining the function.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. No feature described in the context of anembodiment is to be considered an essential feature of that embodiment,unless explicitly specified as such.

Although steps of methods according to some embodiments may be describedin a specific sequence, methods of the invention may comprise some orall of the described steps carried out in a different order. A method ofthe invention may comprise all of the steps described or only a few ofthe described steps. No particular step in a disclosed method is to beconsidered an essential step of that method, unless explicitly specifiedas such.

Although the invention is described in conjunction with specificembodiments thereof, it is evident that numerous alternatives,modifications and variations that are apparent to those skilled in theart may exist. Accordingly, the invention embraces all suchalternatives, modifications and variations that fall within the scope ofthe appended claims. It is to be understood that the invention is notnecessarily limited in its application to the details of constructionand the arrangement of the components and/or methods set forth herein.Other embodiments may be practiced, and an embodiment may be carried outin various ways.

The phraseology and terminology employed herein are for descriptivepurpose and should not be regarded as limiting. Citation oridentification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the invention. Section headings are used herein to ease understandingof the specification and should not be construed as necessarilylimiting.

The invention claimed is:
 1. An integrated multi-channel optical modulefor controllably mapping sets of input light signals onto sets of outputlight signals, the optical module comprising: at least two opticalchannels configured to allow directional propagation of light therein,wherein at least one of said optical channels is an amplificationchannel configured to allow amplification of light propagating thereinby a controllable amplification factor; at least two input ports,individually associated with said at least two optical channels,configured to allow transmission of input light signals into saidoptical channels; at least one output port optically associated with oneof said optical channels, configured to allow emission of an outputlight signal from said one optical channel; at least one control portfunctionally associated with said amplification channel and configuredto allow inputting a control signal to said amplification channel todetermine said amplification factor; wherein said optical channels areoptically coupled so that a power of an output light signal emitted fromsaid output port is a function of powers of said at least two inputlight signals transmitted through said at least two input ports, whereinsaid optical module is a multi-core optical module comprising at leasttwo cores configured to allow directional propagation of light therein,wherein at least one of said cores is an amplification core, whereinsaid input ports, output ports and control ports comprise exposed endsof said at least two cores, and wherein said at least two cores areoptically coupled through evanescent wave coupling.
 2. The opticalmodule of claim 1, comprising at least two output ports opticallyassociated with said at least two optical channels respectively.
 3. Theoptical module of claim 2 comprising M output ports optically associatedwith M of said at least two optical channels, and N input portsoptically associated with N of said at least two optical channels,wherein 2ã‰αM<N.
 4. The optical module of claim 1, wherein the at leastone amplification core is configured to amplify a λ1 light—being lightat a first wavelength λ1 propagating therethrough—by a controllableamplification factor determined by a power of a λ2 light—being light ata second wavelength λ2—propagating therethrough simultaneously with theλ1 light.
 5. The optical module of claim 4 wherein said amplificationcore is doped with ions excitable by the λ2 light and spontaneouslyemitting upon relaxation the λ1 light.
 6. The optical module of claim 4wherein said multi-core optical module is a multi-core optical fiber. 7.The optical module of claim 4 wherein said multi-core optical module isa multi-core photonic crystal.
 8. The optical module of claim 4 whereinsaid λ2 light has a wavelength of about 980 nm and said λ1 light has awavelength of about 1550 nm.
 9. The optical module of claim 1 whereinsaid optical module is a photonic crystal comprising a body bounded byfaces and comprising a periodic structure of a dielectric material, andcomprising optical channels defined by line defects in said periodicstructure formed as tunnels therethrough, said optical channels compriseamplification channels configured to controllably amplify a light signalpropagating therethrough, wherein said optical channels merge injunctions, thereby optically couple and forming a net extendingcontinuously in between said faces, said net comprising at least twoinput ports on said faces, configured to enable transmission of inputlight signals to at least two optical channels of the net, and at leastone output port on said faces enabling to emit an output light signalfrom said optical channel of the net.
 10. The optical module of claim 9wherein said body is a slab and said periodic structure of dielectricmaterial comprises an array of hollow tubes extending between two facesof said slab being thereby periodic in two dimensions.
 11. The opticalmodule of claim 9 wherein said periodic structure of dielectric materialis periodic in 3 dimensions and said photonic crystal is a 3D photoniccrystal.
 12. An optical computation device comprising the optical moduleof claim 1, an array of controllable light sources, said light sourcesbeing selectively optically associated with said input ports, and lightdetectors being selectively optically associated with said output ports,and a control signals interface functionally associated with saidcontrol ports, and a controller functionally associated with said lightsources, light detectors and control signals interface, said opticalcomputation device being configured to produce a calculation byinputting input signals and control signals to said optical module andobtaining output signals therefrom said output signals being a functionof said input signals, said function being determined by said controlsignals.
 13. An artificial neural network comprising the opticalcomputation device of claim 12 and a processor functionally associatedwith a memory and with said controller and configured to implement alearning algorithm.
 14. The optical computation device of claim 12wherein said light sources comprise a Spatial Light Modulator (SLM) forgenerating a multitude of controlled light beams individually opticallyassociated with said input ports, respectively.
 15. The opticalcomputation device of claim 12 wherein said SLM is a Digital microMirrors array Device (DMD).
 16. The optical module of claim 1,configured to switch functionality between an OR gate and an AND gate ofthe at least two cores thereby establishing a Field-Programmable GateArray.